Jet Aerospace designed, analyzed, fabricated, and tested this thruster in September 2005. The decomposition of a mono-fuel, like hydrogen peroxide or nitrous oxide, might be a good choice for small impulse thrusters. Although the specific impulse will be considerably less than that of popular hypergolic combinations like monomethyl hydrazine and nitrogen tetroxide, the processing simplicity of propellants like nitrous oxide might outweigh performance limitations.
The application for a thruster of this size would be for small satellite attitude adjustment. As the intent of the thruster is to fire in small intermittent bursts, there is no integrated cooling system. The thruster was tested with a fixed mass, high pressure gas charge. The gas was heated in the injection system and passed through a metal oxide catalyst bed. Heat is generated in the catalyst from the decomposition of the nitrous oxide into nitrogen and oxygen. The performance of the thruster and transient behavior of the catalyst was tested by measuring temperature change across the catalyst and pressure drop across the nozzle.
The testing program consisted of propellant cold-flow and thruster hot-fire testing. The cold-flow tests were used as a benchmark for a no-reaction condition. Hot-fire tests were run with several injector temperatures and catalyst preheat purge conditions. The thruster produced an average specific impulse of 157 seconds at 0.14 pounds of thrust with pulse duration of 0.6 seconds. Although the specific impulse of the overall thruster is relatively high, some portion of the impulse was provided by resistojet type thrust from injector heating. However, the nozzle inlet temperature profile suggests some level of N2O decomposition and heat generation in the catalyst bed. Maximum gas injection temperature was measured at 678 degrees Fahrenheit at the beginning of gas pulse. The calculated nozzle throat velocity was somewhat lower than expected with a Mach number of 0.61 (with respect to local conditions). The lower than expected nozzle throat velocity shows that the nozzle throat sizing was somewhat optimistic based on pretest flow calculations. The exhaust gas did not luminesce in any of the tests.
Weight |
2.5 lb |
|
Chamber Dimensions |
7.45" L / 1.65" D |
|
Propellant |
Pulsed Gaseous Nitrous Oxide (N2O) |
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Reaction Chamber |
Insulated Pressure Vessel |
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Chamber Cooling |
None |
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Nozzle |
Convergent / Divergent |
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Reaction Initiation |
Resistance Heated Propellant Injection |
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Instrumentation |
Temperature, Pressure |
Years(s) Built |
2005 |
|
Number of Test Runs |
12 Cold Tests |
|
Intent of Design |
To test performance of nitrous oxide mono-fuel thruster |
|
Testing Results |
Maximum Specific Impulse of 157 seconds |
jetman@jetaerospace.org